The following relates to the stereoscopic display arts, virtual reality arts, augmented reality arts, three-dimensional (3D) television or 3D movie arts, and related arts.
Stereoscopic display devices provide a three-dimensional (3D) view by presenting different left and right images to the left and right eyes, respectively. The left/right images correspond to the difference in vantage point due to a (typical) spacing distance between the left and right eyes, and thus the brain processes the left and right images viewed by the left and right eyes, respectively, into a perceived 3D image.
One type of stereoscopic display device, commonly referred to as a head-mounted display device, is in the form of head-mounted gear with physically separate left and right images presented on a display screen or screens, presenting left and right images to the left and right eyes, respectively. The two images are placed close to the respective eyes in order to provide a compact head-mounted display. As the human eye cannot focus too close to the eye (i.e., there is a minimum gaze distance for focusing), the head-mounted stereoscopic display device usually includes eye accommodation lenses interposed between each eye and its screen that provides eye accommodation to an apparent display distance, e.g. on the order of 1.5 meters in some designs. Head-mounted stereoscopic display devices are commonly used in stereoscopic display applications such as immersive virtual reality (VR) headsets or augmented reality (AR) glasses that project 3D images onto the wearer's view of the world.
In another type of stereoscopic display device, the two individual eye side-by-side images are replaced by a larger single screen, such as a television screen, that is simultaneously viewed by both the left and right eyes. This single screen is designed to output the left and right images with different optical polarizations, e.g. the left image may be shown on the screen with left-circular polarization (LCP) while the right image may be shown on the screen with right-circular polarization (RCP). The left and right image frames may be output time sequentially at a “frame rate” greater than the visual response time, e.g. 25-30 frames per second or faster. The viewer wears glasses with appropriate (mutually orthogonal) circular polarizers for the left eye and the right eye, so that the left eye views only the LCP left image while the right eye views only the RCP right image. In an alternative design, polarization-based eye selection is replaced by high-speed optical shutters built into the glasses worn by the viewer and synchronized with the sequential left/right frames displayed by the screen. In these types of stereoscopic display devices, eye accommodation lenses may not be needed due to the larger viewing distance of the single screen. This type of stereoscopic display device may be used in 3D television or movie theaters.
However, a problem arises in such stereoscopic display devices as pertains to gaze distance. As the viewer gazes at various objects shown by the stereoscopic display device, the eyes automatically attempt to focus at the appropriate apparent distance of the object in the perceived 3D space. (This is appropriate function in the real world, where the eyes naturally focus at the gaze point.) However, the left and right images being viewed by the respective left and right eyes (and which the brain perceives as the stereoscopic 3D image) are not actually at that apparent gaze distance; rather, the left and right images are actually at the display screen distance (or at the apparent display screen distance, in the case of a head-mounted stereoscopic display device with eye accommodation lenses). If the eyes focus at the apparent distance of the object then the actually viewed left and right images become defocused, causing blurriness or other visual distortion. In some physiological vision models, it is believed that the actual behavior is more complex, e.g. the eyeballs rotate to the perceived distance but the eye lenses attempt to focus to produce sharp edges in the focused image. The overall effect is unnatural viewing that can cause eyestrain and general feelings of discomfort.